Typical hybrid powertrain systems utilize a combination of an internal combustion engine and an electric engine to provide power to a vehicle. Depending upon the configuration of the powertrain, the internal combustion engine may be configured to provide power directly to the vehicle or the internal combustion engine may be configured to charge a battery used by the electric motor.
Internal combustion engines are well known in the art and operate by burning fuel to create mechanical energy. The efficiency of the combustion of the fuel is measured by the thermal efficiency of the engine. Two types of thermal efficiency are generally considered for an engine, the indicated thermal efficiency and the brake thermal efficiency. The indicated thermal efficiency is determined by the work done by the gases in an engine cylinder and the brake thermal efficiency is determined by the work done at the output shaft of the engine.
During operation of traditional internal combustion engines, approximately between twenty-five and thirty-five percent of the fuel energy leaves the engine in the form of exhaust enthalpy, or wasted energy in the exhaust gas. Accordingly, what is needed are methods and systems for improving the brake thermal efficiency of internal combustion engines in hybrid powertrain systems by reducing the energy lost in the form of exhaust enthalpy.